1. Field of the Invention
The present invention relates to an optical deflector that deflects incident light, a method of producing the same, and an optical device using the same.
2. Related Background Art
In recent years, with the development of microelectronics as represented by the increasing integration density of semiconductor devices, various devices have been enhanced in capability and reduced in size. For example, image display devices, such as laser beam printers and head-mounted displays, and optical intake units or the like of input devices, such as barcode readers, in which an optical deflector is used for optical scanning, have also been enhanced in capability and reduced in size and are being required to be further down-sized. Optical deflectors meeting such a requirement have been proposed in Japanese Patent Application Laid-Open No. 6-82711 (no corresponding document in foreign language) and Japanese Patent Application Laid-Open No. 2000-147419 (no corresponding document in foreign language), for example.
FIG. 16 is a perspective view of a first conventional optical deflector disclosed in Japanese Patent Application Laid-Open No. 6-82711.
A scanning mirror 1001 of the optical deflector is in the form of a rectangular plate and comprises a glass plate 1009, a mirror part 1002 capable of reflecting a light formed on one side of the glass plate by evaporation of aluminum or the like, and a rare-earth permanent magnet 1003, such as a samarium-cobalt (SmCo) magnet, formed in the shape of a thin film on the other side of the glass plate by sputtering or the like. Supporting members 1004 in the form of strips made of a metal, for example stainless steel or beryllium copper, are each fixed, at one end thereof, to the center of both longitudinal ends of the mirror part 1002 and supported thereon and fixed, at the other end thereof, to a device main body (not shown). The angle of the scanning mirror 1001 can be changed around a torsion axis 1005 connecting the supporting members 1004 by torsion of the supporting members 1004. The permanent magnet 1003 is magnetized so as to have opposite polarities on both sides of the driving axis 1005, as shown in FIG. 16.
Furthermore, a magnetism-generating unit 1006 comprises a coil frame 1008 and a coil 1007 wound around the coil frame and is disposed at a predetermined distance from the side of the scanning mirror 1001 on which the permanent magnet 1003 is formed. Therefore, when the coil 1007 is energized, the magnetism generating unit 1006 generates magnetism, and an attractive or repulsive force arises between the magnetic poles of the permanent magnet 1003 and the magnetism generating unit. The force activates the scanning mirror 1001 and displaces the same to any angle according to the magnetism generated by the magnetism generating unit 1006.
FIG. 17A is an exploded perspective view of a second conventional optical deflector disclosed in Japanese Patent Application Laid-Open No. 2000-147419, and FIG. 17B is a schematic sectional view taken in the longitudinal direction of the optical deflector of FIG. 17A.
As shown in FIG. 17A, an optical deflector 2001 has a planar rectangular base 2002. A ridge 2003, formed integrally with the base 2002, protrudes from the entire outer periphery of the base 2002, and a vibration unit 2005 is provided on the ridge 2003.
The vibration unit 2005 comprises a rectangular outer frame 2006, a reflective mirror 2007 having a reflective surface 2007a formed thereon and disposed in an opening 2006a of the outer frame 2006, and a pair of supporting parts 2008 that couples the reflective mirror 2007 and the outer frame 2006 with each other along an axis substantially passing through the center of gravity of the reflective mirror 2007. The outer frame 2006 is fixed to the ridge 2003, and the reflective mirror 2007 can be swung around the pair of supporting member 2008 serving as a torsion axis CL.
On the back surface of the reflective mirror 2007, there is formed a mirror-side comb section 2009 composed of a groove 2009a and a projection 2009b extending in a direction perpendicular to the torsion axis CL. A pair of fixed electrodes 2010 and 2011 is disposed on the base 2002 so as to be in opposition to the mirror-side comb section 2009 of the reflective mirror 2007, and also on the upper side of each of the paired fixed electrodes 2010 and 2011, there is formed an electrode-side comb section 2012 composed of a groove 2012a and a projection 2012b. The mirror-side comb section 2009 and the electrode-side comb section 2012 are disposed in such a manner that the groove 2009a and the projection 2009b engages with the groove 2012a and the projection 2012b. Further, as shown in FIG. 17B, between the fixed electrodes 2010, 2011 and the reflective mirror 2007, a voltage can be applied selectively via switches SW1, SW2, respectively. Therefore, alternately turning on and off the switches SW1 and SW2 to alternately apply a voltage to the paired fixed electrodes 2010, 2011 can swing the reflective mirror 2007 around the torsion axis CL corresponding with the paired supporting members 2008.
However, these first and second conventional examples have problems described below.
In the first conventional example, to activate the mirror part 1002 at a high speed and with a large angle of deflection, it is desirable that the moment of inertia of the scanning mirror 1001 around the torsion axis 1005 is small. A possible approach for reducing the moment of inertia of the scanning mirror 1001 in the arrangement according to the first conventional example is to reduce the thickness of the supporting members 1004. However, if the thickness of the supporting members is reduced, the rigidity thereof is also reduced. Therefore, when the scanning mirror 1001 is activated to torsionally vibrate at a high speed, the scanning mirror 1001 significantly fluctuates in position because of the inertial force caused by the self-weight thereof. Thus, there is a problem that it is difficult to provide both of action of the scanning mirror at a high speed and with a large angle of deflection and optical characteristics of the optical deflector.
In addition, if a high magnetism generating power is required, the thickness of the permanent magnet 1003 has to be increased. Thus, there is another problem that the moment of inertia of the scanning mirror 1001 significantly increases, and the center of gravity of the scanning mirror 1001 is largely displaced from the torsion axis 1005 and a stable torsional vibration cannot be attained.
In the second conventional example, to activate the reflective mirror 2007 with a large angle of deflection, the projection 2009b of the mirror-side comb section and the electrode-side comb section 2012 are required to have a sufficient height in order to avoid interference between the reflective mirror 2007 and the base 2002. Thus, there is a problem that the moment of inertia of the reflective mirror 2007 inevitably increases as the angle of deflection increases, and it is difficult to provide both driving characteristics of high speed and a large angle of deflection.
In addition, in the second conventional example, since an electrostatic actuator requires a higher voltage than an electromagnetic actuator, the power supply unit inevitably has a large size. Thus, there is a problem that, even if the optical deflector can be reduced in size, the driving unit still has a large size, and the size of the whole device is still large.